PHS is a portable low power cellular phone developed by Japan NTT Corporation. PHS handset is also called “little cellular phone” in Taiwan. Since the power being utilized in PHS handsets belongs to low power system, PHS handsets are not suitable being used under high speed movement environments. Conventionally, the transmission power of a base station of PHS is no more than 32 W, of which the frequency is in a range of 1,895 MHz to 1,918 MHz, and the data transfer speed is in a range of 64 Kbps to 128 Kbps. In view of the above data, a person driving a car on a highway in a speed below 120 Km per hour still can use a PHS handset to send e-mails, pictures, messages, etc. However, if the car is in a speed above 120 Km per hour, it will be difficult for the PHS handset to receive or transmit the corresponding signals without being interfered.
Moreover, since PHS has the features of low power, large system capacity, and high data transmission rate, PHS is thus particularly suitable for metropolises. Also, there are other features, such as its charge is relatively low, its electromagnetic interference is very small, and its Internet access rate is about 64 Kbps. Most importantly, its design is diversified. Due to the above features, PHS handsets are now widely popular among young people and available in the market.
However, the ring circuit and the receiver circuit of a typical PHS handset are separate in its circuitry, wherein the power of ring signal generated by the ring circuit is amplified by a voice-frequency amplifier, and the voice corresponding to the amplified ring signal is then produced by a speaker having an electrical resistance of 8 Ω. As for the signal being received by the receiver circuit, it is amplified by another voice-frequency amplifier to a low power signal applicable to telephoning, and the voice corresponding to the low power signal is then produced by another speaker having an electrical resistance of 32 Ω. For having a sufficient volume in order to inform a user to answer the telephone, a peak power of the amplified ring signal is typically in a range of 400 mW to 500 mW (in a load of 8 Ω). Sound volume should be optimum, preferably the amplified receiver signal has a peak power in a range of 20 mW to 40 mW (in a load of 32 Ω) since the receiver is close to the ear in telephoning. In view of the above, it is found that the volume difference between these two speakers is significantly large. However, as stated above, the ring circuit and the receiver circuit of a typical PHS handset are separate in its circuitry, resulting in the increase of the circuitry design cost and the manufacturing cost due to the requirement of two voice-frequency amplifiers and two speakers having different electrical resistances. Hence, a need for reducing the unnecessary cost exists.